Trachoma is a chronic kerato-conjunctivitis caused by the intracellular bacterium Chlamydia trachomatis. In the nineteenth century it was an important cause of blindness in Europe and North America, but it disappeared from more affluent parts of the world as living standards improved in the twentieth century. It is now a disease of poor rural communities, mainly in Africa and Asia, but it remains the leading infectious cause of blindness worldwide (Mabey et al. 2003).